Figure 1.

The Pseudomonas fluorescens experimental system studied by Brockhurst et al. [5]. (a) The 'wrinkly-spreader' variant of P. fluorescens constitutively produces extracellular polymers that bind cells together and provide
structural support for biofilms that reside at the liquid-air interface of medium
in glass beakers. (b) Such biofilms are susceptible to invasion by mutants that do not secrete extracellular
polymer, which eventually compromise the integrity of biofilms, causing them to sink
into the liquid phase below. Photographs courtesy of Paul B Rainey.